The act of slapping two penises together. Learned people (that's "learNED" pronounced with two syllables, boyee) often use the word "discourse" because they do not want to offend anyone by actually saying "slapping two penises together."

Eagleton is invoking an ethical obligation on the part of the intellectual to speak for, but also to, those whose consciousness is lagging behind whatever Hegelian discourse of utopian progress is being espoused.